The 2015 general election will be thrown into turmoil if Scotland votes for independence in September’s referendum, according to government legal advice.

An election is scheduled to be held on May 7 next year but by then Scotland could already be preparing to separate from the rest of the United Kingdom.

The leading lawyer who wrote the Westminster government’s legal advice on Scottish independence is now warning that a “Yes” vote in the referendum would have major ramifications for the election, and could destabilise the next British government.

Cabinet ministers fear that if Alex Salmond’s independence campaign succeeds, the general election would be in grave doubt, plunging Britain into an unprecedented “constitutional crisis”.

In a memorandum for the House of Lords, Professor Alan Boyle, a specialist in international law at Edinburgh University, outlined two options for the election if Scotland chooses independence on September 18.